1. Field of the Invention
The present invention relates to a phase array antenna comprising a plurality of dipole means according to claim 1.
2. Description of the Related Art
A dipole antenna is known from U.S. Pat. No. 5,021,799. This US-patent discloses a dipole antenna, in which the first line and a second line of a microstrip transmission line means are tapered to provide a microstrip-to-balanced line impedance transformation. Further on, the first and the second line are separated in the direction of the dielectric substrate middle plane, form an electric field and provide an impedance transformation from an unbalanced line part of the microstrip transmission line means to first and second balanced dipole antenna elements. Therefore, in the antenna disclosed in U.S. Pat. No. 5,021,799, the transformation from unbalanced to balanced transmission is conducted within microstrip transmission line means of the dipole antenna. Also, this antenna is inherently selective (not wide band) due to the classic dipole microstrip structure. Further on, this known antenna is tolerance sensitive. The thickness of the substrate of this known antenna is 0.0125 wavelength, that would lead for the 60 GHz range to a thickness of 0.0625, which is very thin and critical to be manufactured and handled. However, due to the specific structure of the dipole antenna disclosed in U.S. Pat. No. 5,021,799, the dipole antenna can be mainly applied for narrow band applications. The manufacturing tolerances, increased losses in dielectric material, decreasing of the substrate thickness, supporting the substrate with the same distance to the reflector plane, as well as possible appearance of the high order modes limits its application in the lower microwave range (3-30 GHz).
U.S. Pat. No. 4,737,797 discloses a dipole antenna without a reflector plane. This dipole antenna comprises a transmission part within the microstrip transmission line means, in which signals are converted from an unbalanced line to a balanced line to permit the signal to be radiated by first and second balanced dipole elements. The dipole antenna disclosed in U.S. Pat. No. 4,737,797 exhibits a wide band width up to 1.7 GHz (about 30%). However, the dipole antenna does not allow applications up to the millimeter wave range, because of very critical tolerances (thin traces) for balun-circuits and very thin substrates (like 0.024 mm for 60 GHz), where a physical support of the structure (robustness) and availability of such small dielectric thickness is questionable.